1. Field of the Invention
The invention relates to the cementing of well conduits in well bores by cement supplied through a substantially smaller diameter tubular member extended concentrically downwardly through the conduit.
2. Description of the Prior Art
The practice of cementing the bottom portions of well casings or conduits in wells is commonplace. When wells were drilled to accommodate moderate size casing diameters in the range of four to seven inches, it was expedient to supply the cement for the cementing operation by pumping the cementing fluid directly through the bore of the installed casing. As casing sizes and well depths have increased, it has become increasingly difficult to utilize the entire casing bore as a conduit for the cementing fluid due to the large quantities of cementing fluid that are required to be transmitted through the casing bore and to the excessively large pressures required to force that large fluid volume of cementing fluid outwardly around the exterior of the casing. Furthermore, the entire casing bore has to be carefully wiped subsequent to the cementing operation and no wiping operation is perfect, thus resulting in patches of cement film being adhered to a large number of regions of the casing bore which would substantially interfere with the deployment and setting of tools normally required to place a well in production.
In recent years, it has been the practice to accomplish the cementing of large diameter well casings by running in a drill pipe or other tubular member to the bottom of the casing or other conduit and supplying the cementing fluid through the smaller diameter drill pipe. The small drill pipe can withstand the higher pressures required to effect the desired distribution of the cementing fluid. Furthermore, after the cementing operation, the drill pipe can be removed and the fact that the bore of the drill pipe is not cleanly wiped is immaterial insofar as the subsequent operations on the well are concerned.
Even with drill pipe application of cement, there is a pracactical limit to the amount of cement that can be caused to flow upwardly around the exterior of the well casing. It therefore becomes desirable to effect the cementing of the well through the drill pipe in at least two stages. In the first stage, the cement is discharged into the well bore through an axial cement conduit formed in the bottom of the casing. In the second stage, cement is discharged through radial ports provided in the well casing at a position above the level of the cement introduced during the first stage operation. The radial cement ports obviously have to be sealed during the first stage cement operation and then resealed at the conclusion of the second stage cement operation.